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not capable of drawing air in through ductwork on the intake or discharging air through
ductwork on the exhaust. The discharge air will be significantly warmer than the intake air.
Evaporator
The standard evaporator is constructed of stainless steel plates and copper brazing. (An
optional “nickel brazed” evaporator is available with the high purity construction option.) The
refrigerant passes between every other set of plates, while the coolant flows on the other side
of the plates in the opposite direction.
Thermostatic Expansion Valve
This valve (referred to as the TXV) separates the high pressure/high temperature side of the
refrigeration circuit (the condenser side) from the low pressure/low temperature side of the
refrigeration circuit (the evaporator side). The TXV maintains constant superheat at the
evaporator outlet, regardless of process load, by precisely metering the amount of refrigerant
into the evaporator. Superheat is the difference between the saturated evaporative
temperature and the actual measured temperature at the TXV sensor bulb. The superheat is
factory set for 10°F to 12°F (5°C to 6°C) and should never exceed 15°F (8°C). Only a trained
refrigeration technician should adjust refrigeration system valves.
Refrigerant Sight Glass
The refrigerant sight glass is located in the liquid line ahead of the expansion valve. It allows
the operator or service technician to observe the flow of liquid refrigerant. Prolonged periods
of foaming in the sight glass may indicate a low refrigerant condition or a restriction in the
liquid line. Occasional bubbling in the sight glass may occur at a time when load conditions
are changing and the thermostatic expansion valve is adjusting to the new conditions. This
momentary occurrence is a result of normal chiller operation. The sight glass can also be
used to check if there is moisture in the refrigeration system. If there is moisture in the
system, the green dot in the center of the sight glass will turn yellow. If this occurs, the chiller
should be serviced immediately.
Refrigerant Filter Drier
The filter drier is located in the liquid line between the condenser and the refrigerant sight
glass. It is designed to remove any moisture and/or foreign matter that may have gotten into
the refrigerant stream. Moisture and foreign matter can cause serious damage to the
components of a refrigeration system. For this reason, it is important that the chiller be
equipped with a clean filter drier. Replace the filter drier if any of the following conditions
occur:
1. The refrigeration system is opened to the atmosphere for repairs or maintenance.
2. Moisture is indicated in the sight glass (the green dot has changed to yellow).
3. An Excessive pressure drop develops across the filter drier. This is indicated by a
significant temperature difference between the filter inlet and outlet.
Pressure Relief Valve / Blow Out Plug
The pressure relief valve is located in the liquid line after the condenser. It is designed to
relieve refrigerant pressure under severe conditions in order to protect the refrigeration circuit
components from damage.
Hot Gas Bypass Valve
This valve is located in the refrigerant line that runs from the compressor discharge to the
evaporator inlet. It is designed to artificially load the chiller when the chiller is catering to a
partial load from the process. This is accomplished by directing some of the hot compressor
discharge gas directly back into the evaporator instead of going through the condenser. The
microprocessor based PID temperature controller controls the amount of hot gas used.
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